The narrowest optical filter bandwidths are obtained with atomic line filters (ALF's) which have acceptance bandwidths on the order of 0.001 nm. In prior art, ALF's, broadband light containing narrowband signal light is passed through a color glass filter which cuts off wavelengths below a threshold value. The signal and remaining noise light enter an atomic vapor that only absorbs the signal light within the atom's 0.001 nm acceptance bandwidth thereby exciting those absorbing atoms to an intermediate energy level. A pump beam further excites these atoms to a second, higher energy level that then decays through various processes including fluorescence, to the ground state of the atom. The emitted fluorescence occurs at wavelengths below the threshold value. A second color glass filter then cuts off any wavelengths above the threshold which effectively permits passage of only the emitted narrowband fluorescence. In effect, the incoming signal has been internally shifted in wavelength by the atomic vapor, which then allows the use of two overlapping color glass filters to block any background radiation. For some applications these filters have two drawbacks, slow response time (about 500 ns for the alkali atoms) and low quantum efficiency which is defined as the ratio of the number of fluorescence photons detected to the the number of incoming signal photons. A need exists for a light filter that retains the acceptance bandwidth of an ALF but has a faster response time and higher quantum efficiency.